Damping material for telephone.



E. H. CRANDALL. DAMPING MATERIAL FOR mmromm APPLICATION FILED AUG. i4.I516- Patnited Feb. 12, 1918.

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Epecification 0! letters Patent.

Application filed August 14, 191s. Serial No. 1 1,795.

To all whom it may concern:

Be itknownthat I, IRVING- B. CRANDALL, a citizen of'the United States,residing at New Yorlm in the county of New York. and. State of New York,have invented certain new (the! usefullmprovements in Damping Materialfor Telephone, of rhich the following 1s a. full, clear, conclsc, andexact description.

Thisilwcntion relates to scund absorbing materials and to the damping ofvibratij cg members, and in particular to vibrating i121- phragmssucliss are used in teleyhonic ccmmuriicstion in phonogrophs, etc. itsob ject is to so damp the vibrat ons of such acrghrcg'ms. as to suppressthe tendency of these cles.

In'telephcneprsctice, has been found that; diaphraqms, both forreceivers and transmitters, haves more or less marked mtumlperiod andthis is usually in neighborhood of 900 cycles per second. Thecharactefifiic of diaphmgms to x'espoi d more strongly toicscillatioilsat s c period fcs'use's'jo distortion tl'EQSUIlfi pulses impres ed; onthem and the-geby' iapliragms to vibrate WT (t; certain frequenspeech.The invection, then, has for its pm"- pose primarily to Iii-k6liIlQT-DVQHIBETRS the quality, of's'pc sch'as transmitted by prsvimzstelephonic or phcnogrsphio apparatus, and acccmpiishes'this purpose bydecreasing the tendency of the vibrating parts to scape-mi to ccrtoinfrequencies.

' The inventions ill be better uncle-m5 "c1;

reference to the. v'toi lowiiig specification anilvaccompanying-drawing, in 'WhlClL-Fl 'UIE i ,may be present in,diapiircg, 4.- i l v with dxfi'ere it :dcgrees of clamping, rigs; ,2:

vstricl 3,sl ow forms of e telephone transmitter and receives-embodyingthis invention,

lleiecrin m Fig 1', it will be seen tl ot ftequenc les'cce mdmoted asfilJSCIS$E and "r' Elie pitch or frequency would be brought out to therelative detriment of other frequencies. Such diulrin-agms, furthermore,could be obtcinccl only 'Wl'tll some diiiiculty and by special pi-cwision. In general, telephone die pliragzns (10 not have such amarked resonance as indicated by this curve, but their resonancecharacteristic woulci iris-indicated more correctly by curve B becauseof vs- )TlOilS frictional forces. Even with such a diaphragm, however,it would be noted that over certain limited range of frequencies ponscis much greater than for other and speech transmitted by such diaphragmshows a considerable amount of distortion and corresponding dccreese in.the quality of tmnsmission. The ideal disphrogm should have a resonancecurve represented by a line which is parallel to' the horizontal axis,indicating an equal response to all frequencies It is. however,impossible to obtain such a diaphragm, but with this invention, it ispossible to cause a cliapiii'sgm to vibrate with a characteristic suchas shown in curve C, which is a close approximotion to the idesicondition.

C} may be obtained by increasing the damping ctor of the diaphragm. Ingeneral, the (1 mping factor of any vibrating system depends oniy uponthe frictional forces anti upon the inertia. being proportional to thefrictional forces and inversely propoitioflsl to the inertia or mass ofthe system. A slic plim 13 having resonance characteristic as given by3} C0lll-fi therefore lie ange to approach of the diaphragm orbyincrcasing the fricticn z'zi forces. Attempts have been made to obtaina, fiettei" charoctcristic by changing both the "frictional forces andthe 1 1 ice fricticnai forces .by the use of damping ended with acertain measure' of success.

Isltt and similaz' material possess acerta-in amount of elasticitytlicmsclvcsjapd us'gsuch are not ideal clamping materials.

is has beccfound the: very smooth, finely Patented Feb) is, time;

the rescn once elismcstlc G oydccresling the inertia-or mass- .80 Achange from the curve B to the curve but it has been :fcuncl that l'imt'zs sejon reached. Vat-i :ngs 0!: strips or rings of felt or othcz:

iics been found, however, that rings of? divided, non-packing metallicpowders, of such metal as copper, magnesium, aluminum and so forth, butin particular aluminum and magnesium powder, posses an exceedingly smallamount of elasticity, and. taken in mass, submit to distorting ordisplacing forces very readily with a remarkably small tendency toreturn. to their former position.

.This invention consists, then, in the above discovery, and in itsapplication .to the damping or vibrating members. One manner of itsapplication 15 ndicated 1n Fig. 2,

in which 10 rcprcsentsa suitable diaphragm of the usual type used intelephony. 11 represents a. shell or case supporting and containing theusual electromagnet 12 for receiving or generating telephonic currents.

As such, this device constitutes a well-known form or telephone receiveror transmitter. 'Within this shell or container, and].completcly fillingthe same so as to be in inti mate contact with the shell and with thediaphragm 10, is placed finely divided or powdered aluminum or magnesium13, and

it is found as a result. that the diaphragm '10 is enormously damped andresponds al-' most equally to all vibrations impressed thereupon, theresonance curve bcin similar to that shown at. C in Fig. 1. While I haveinparticular mentioned aluminum and magnesium, I find of the two that.aluminum'is preferable in that it has both a very low times this value.

- )5Y hil e this invention mass and a very low elasticity.

. Fig. 3 shows a similar application of this ,inventionto a well-knownform of micro- .phonc transmitter and it 1s apparent. from 'sheea shewpplicd in niit'ieu'lar' to a telephone transmitfit maybe equally.ivcllap-plicd in numerous other .forms appa|'atus-such, for ex- "ample,as phonograph diaphragms and other places in which it is desired, foronereason or another, to have. large damping for vi J bra ting parts.- i

" fife- -This damping material may also he used in J'inalci'ng'souml-proof cavities or spaces,

; bcinguscd, for example, as a iillcr lwtwren twowalls surrmmding saidcavity or space. Having now described this invention,

tcr or rccciver, it is to be. understood thatwhat I claim to'be new anddesire to secure by Letters Patent is:

1. A device for converting mechanical vlhrations and electrical impulsescomprising a. mechanically vibrating member, an electrical translatingdevice associated therewith, and independent means for damping thevibration of said member, said inde: pendent means consisting of afinely divided metal.

2. A device for converting mechanical-vi brations and electricalimpulses comprising a mechanically vibrating member, anelectricaltranslating device associated therewith, and independent means fordamping the vibration of said member, said independent means consistingof a finely divided mass of aluminum or magnesium,

3. A device for converting mechanical vibrations and electricalimpulses'comprising a mechanically vibrating diaphragm, an electricaltranslating device opcratively as sociated with a portion of onesurface'of said diaphragm, and independent means for damping thevibration of said diaphragm, said means consisting of a finelydividedmetal in contact with substantially all 01 the remainingvibratory portions of said surface not associated with'said electricaltranslating device.

4. In apparatus members, means for transmitting the vibration of saidmembers, and independent means for damping the vibration of saidmembers. said independent means consisting of a finely divided metal.

Fain apparatus comprising vibrating nunnbersfmeans for transmitting thevibrations of said members,and/independent means 'For damping thevibrations oi. said members. said independent means consisting of afinely divided mass of aluminum or magnesium.

comprising vibrating 6. In apparatus comprising a vibrating diaphragm,means operatively associatedwith a portion offlonc surface of said.diaphragm for transmitting the vibrations of said diaphragm, andindependent. means fol damping thevibrations of said diaphragm, saidindependent means consistin of finely divided metal in contactwith sustantiallyall remaining vibrating portions of said surface notassociated with sa'id'vibration trimsmittmg mcansi'i 7. A, telephoneinstrument:comprising a vibrating diaphragm, a variable resistancedcv'icc operative-1y associated with'a portion of'onc surface of saiddiaphragm, and a damping material for said diaphragm inth'ptlulmll'. ofsaid variable resistance device, ..-.i l material consisting-of a finelydivided metal associated with substantially alt-reroaming-vibratingportions of said surface not associated with saidvariabie r sistamue device. v

8. A telephone instruu'lentcomprising a; vibrating diaphragm, a wariablaresistance 5 devie o'p'eratively flSQOCifiEEd with a portian of oneSurface- 01? amid diuplumgm, and a damping material for sum dia Haganindependent ofsaid variable msiswnce device, said material consisting 0ffinely dividefi aluminum or magnesium associatecl with 10 substantiallyall remaining vibrating partinns 01 :said surface not assuciate withsaid variable, ma, gtance device.

In with,v 'whereuf, I hereuntn subscribe my name this 122th day ofAugust A. 1)., 15 1916.,

IE-mm 15., GRANDALIQ

